I think (absolutely not sure) that UFOextender accuracy only applies to XCOM, not to aliens.
wrong. 2 points for correct use of conjecture.
it DOES apply to aliens.
I know that reaction shots are always snap shots for XCom but can be auto-shots for aliens.
wrong. no points awarded due to use of the term: "i know".
ALL reaction shots are snap shots, regardless.
to set the record straight:
yes it affects reaction fire.
yes it affects aliens.
reaction fire can ONLY be snap shot.
The AI chooses which shot type to use based on range, so for all intents and purposes, they account for the difference it makes.